It is known to prepare greases from base oil, an overbased calcium sulphonate thickener as well as conventional thickener such as lithium 12-hydroxy stearate and optionally other performance additives for example antioxidants or antiwear agents. Grease containing an overbased calcium sulphonate thickener is known to have acceptable corrosion inhibiting properties. However, this type of grease has poor water resistance properties such as poor water wash-off or water repellency as shown in an ASTM D4049 water spray-off test. Grease with poor water wash-off or water repellency decreases the longevity of grease and increases wear on the surface being lubricated.
Polymers have also been added to grease, other than overbased calcium sulphonate grease, to improve the performance characteristics of the grease. For example, polymers have been employed to decrease water wash-off, to decrease oil separation, to increase water repellency, to increase dropping points or cone penetration and as thickeners. The polymers are polymethacrylates or polyolefins. Typically these polymers are incorporated in the base oil and act as a viscosity modifier. However, the polymers have limited interaction with the thickener resulting in the grease being more susceptible to the effects of water, for example, water wash-off or decreased water repellency.
U.S. Pat. No. 5,308,514 (Olson et al.) discloses a high performance overbased calcium sulphonate, grease comprising up to about 28 wt % of overbased calcium sulphonate, colloidally dispersed in the calcium carbonate essentially in the form of calcite, a calcium soap of a fatty acid containing about 12 to about 24 carbon atoms and an oleaginous material. The grease has a worked cone penetration rating of less than about 295. The grease contains a polymer with poor water resistance properties.
U.S. Pat. No. 5,338,467 (Olson et al.) discloses a process for preparing a non-Newtonian oil composition in the form of a grease comprising an overbased calcium sulphonate, colloidally dispersed in calcium carbonate in the form of calcite. The grease is prepared by heating the overbased calcium sulphonate amorphous calcium carbonate and a converting agent containing about 12 to about 24 carbon atoms in an oleaginous material. Neither the process nor the final grease contains a polymer capable of imparting water resistance properties.
U.S. Pat. No. 4,597,880 (Eliades et al.) discloses a one-step process for preparing a calcium sulphonate grease or complex grease by admixing a volatile carrier, calcium sulphonate as a dispersing agent and calcium carbonate in the form of calcite. Neither the process nor the final grease contains a polymer capable of imparting water resistance properties.
U.S. Pat. No. 6,300,288 (Scharf et al.) discloses a polyolefin having grafted carboxylic acid functionality capable of imparting water resistance properties into grease. The grease may contain a gelled overbased material containing a number of acidic organic compounds with functional groups including sulphonic acid hydrocarbyl succinic acid or ester thereof, or a carboxylic acid or derivatives thereof. The carboxylic acid includes polyisobutylene succinic acid or polypropene succinic acid.
It would be desirable to have a grease capable of imparting decreased water wash-off. The present invention provides a grease that is capable of imparting decreased water wash-off.
It would be desirable to have a grease that is capable of imparting improved thickening. The present invention provides a grease that is capable of imparting improved thickening.